A lens is a transparent refracting medium bounded by two curved surfaces, of which one or both surfaces are spherical. A lens with both surfaces bulging outwards is called a double convex lens or simply a convex lens. A convex lens converges the light rays incident on it to a point. Hence, a convex lens […]
Sound is produced and is heard when a body vibrates in a medium. When the vibrations reach our ears, a sound is heard. Our ears are sensitive only to a limited range of frequencies, from 20 Hz to 20,000 Hz. Sound of frequency above 20,000 Hz is called ultrasonic, while the sound of frequency below
Machines help us to perform daily activities in a better efficient way. A machine can be defined as a device by which we can either overcome a large resistive force (or load) at some point by applying a small force (or effort) at a convenient point and in a desired direction or by which we
An electromagnet is a temporary strong magnet made of a piece of soft iron when current flows in the coil wound around it. It is an artificial magnet. Electromagnets are mainly used for the following purposes: Electromagnetism PDF Download PDF
When two bodies at different temperatures are kept in contact, heat flows from the body at a higher temperature to the body at a lower temperature. The measurement of heat is called calorimetry. The SI unit of heat is joule (J). The other most commonly used unit of heat is calorie (cal). The heat energy
When a ray of light passes from one medium to another medium, it gets deviated from its path because of the difference in speeds of light in the two media. Newton allowed the white light from the Sun to enter a darkened room through a small aperture in a window and placed a glass prism
Force is a physical cause that changes (or tends to change) either the size or shape or the state of rest or motion of the body. The forces which act on bodies when they are in physical contact are called contact forces. When a body moves over a rough surface, a force acts on the
The substances which disintegrate (or decay) by the spontaneous emission of radiation are called radioactive substances. Examples: Uranium, radium, polonium, thorium, actinium, etc. The isotopes of nearly all the elements of an atomic number higher than 82 (i.e. lead) are radioactive. These are called natural radioactive substances. The phenomenon of radioactivity cannot be due to
Current is the rate of flow of charge across a cross-section normal to the direction of flow of current. It is a scalar quantity. Its SI unit is ampere (A). Current is one ampere if the rate of flow of charge is one coulomb per second. If n electrons pass through the cross-section of a
Power is the rate of doing work, i.e. it is the work done (or energy consumed) in 1 s. In an electrical circuit, we define power as the rate at which electrical energy is supplied by the source. The SI unit of power is watt (W) or J s−1. One watt is the power consumed